Before he launched the most viral video in Internet history, Jason Russell was a half-hearted Web presence. His YouTube account was dead, and his Facebook and Twitter pages were a trickle of kid pictures and home-garden updates. The Web wasn‚Äôt made ‚Äúto keep track of how much people like us,‚ÄĚ he thought, and when his own tech habits made him feel like ‚Äúa genius, an addict, or a megalomaniac,‚ÄĚ he unplugged for days, believing, as the humorist Andy Borowitz put it in a tweet that Russell tagged as a favorite, ‚Äúit‚Äôs important to turn off our computers and do things in the real world.‚ÄĚ

But this past March Russell struggled to turn off anything. He forwarded a link to ‚ÄúKony 2012,‚ÄĚ his deeply personal Web documentary about the African warlord Joseph Kony. The idea was to use social media to make Kony famous as the first step to stopping his crimes. And it seemed to work: the film hurtled through...